Implantable medical devices include cardiac function management devices, such as pacers, cardioverters, defibrillators, cardiac resynchronization therapy devices, or devices having a combination of such attributes. Such devices generally use electrodes, such as for sensing intrinsic electrical heart signals, for delivering stimulations to induce heart contractions, or for delivering a countershock (“shock”) to interrupt a tachyarrhythmia. Such electrodes may include, for example: an intracardiac electrode located within a heart (e.g., on a multiconductor or other intravascular lead); an epicardial electrode located on the heart; or a can or header or other electrode located at or near an electronics unit, which is generally implanted pectorally, abdominally, or elsewhere.
Mechanical stress may affect an intravascular intracardiac lead, having multiple such intracardiac electrodes located at or near its distal end, with multiple conductors leading to a connector at its proximal end, which connects to an implantable electronics unit of a cardiac function management system. Lead failures are a well established problem for the medical device industry. For example, an implantable cardioverter-defibrillator (ICD) lead failure rate of 2.73% at 56 months+/−28 months has been reported. See Dagmara, et al., Occurrence of ICD Lead Fracture Is Related to Foregoing ICD Replacement or Lead Intervention, Heart Rhythm, 2001. 1(1): p. S208-S209. Another example reported a mean time to failure of 6.8+/−5 years for ventricular pacing leads and 6.0+/−4.2 years for atrial pacing leads. See Hauser et al., Clinical Features and Management of Atrial and Ventricular Pacing Lead Failure: A Multicenter Registry Study, Heart Rhythm, 2004. 1(1): p. S13. Lead failures may take several different forms, or failure modes. One example of ICD lead failures were classified as: 43% lead insulation failures, 31% low voltage (e.g., pacing electrode) conductor failures, and 10% high voltage (e.g., shock electrode) conductor failures. See Hauser et al., The Multicenter Registry's Experience with 4,059 ICD and Pacemaker Pulse Generator and Lead Failures, Heart Rhythm, 2005, 2(5): p. S30. Lead failures can result in an apparent short circuit between electrodes, or in an open circuit to one or more electrodes for sensing or delivering electrical energy. This can adversely affect performance of the accompanying cardiac function management system. For example, for a tachyarrhythmia patient with an ICD, a lead failure may result in the ICD inappropriately sensing mere noise as tachyarrhythmic cardiac depolarizations, resulting in unwarranted delivery of a shock. As another example, for a bradycardia patient with a pacer, a lead failure may result in loss of pacing, resulting in inadequate cardiac output for the patient. In sum, lead failures can have serious consequences for patients with cardiac function management devices.